Topic 7 - Modern Analytical Techniques 1
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What can mass spectrometry be used to identify?
• number of isotopes within a sample - relative abundance of each isotope
What are the (5) stages in a mass spectrometer?
• vapourisation • ionisation (by electron bombardment) • acceleration (from electric field) • deflection (from electromagnet -determines mass) • detection (by charged plate -generated potential difference proportional to charge of ion)
How are atoms ionised in a mass spectrometer?
• electrons are fired by an electron gun at the atoms - causes atoms to loose e- (becoming positively charged)
How are ions accelerated in a mass spectrometer?
by an electric field
How are ions deflected in a mass spectrometer?
by a magnetic field
What is a molecule’s fragmentation caused by?
unstable positive ion after electron bombardment
What are the 2 parts to a fragmentation?
• positive ions - free radical
What is the molecular ion (M+) peak equal to?
molecular mass of unfragmented compound
What does a mass spectra show us?
• molecular mass of a compound - information of compound’s structure (using its unique fragmentation pattern)
What is infra-red spectroscopy?
instrumental analysis technique used to identify types of bonds in a molecule -allows us to identify functional groups
What does a bond require to become excited when using infra-red spectroscopy?
a specific frequency in the infra-red spectrum -this energy (frequency/wave number) is absorbed
What is the relationship between wavenumber and frequency?
directly proportional
What does a wavelength absorbed by a bond depend on?
• bond length • bond strength • mass of each atom either side of the bond
What happens when a bond absorbs energy?
the bond does any of three things: • stretches (asymmetric or symmetric) • bend (like a pendulum) • vibrate
What are the two types of bond stretching?
• asymmetric (alternatively stretching and contracting) - symmetric (simultaneously stretching and contracting)
What can an infra-red spectra be used to show?
if a reaction is successful -when a functional group changes, you can tell a reaction has occured
What is the fingerprint region of an infra-red spectra?
an exact pattern of complicated peaks that a particular compound creates -can be used to identify a particular compound
What molecules don’t absorb infra-red and why?
molecules don’t absorb infra-red because the atoms are identical so a dipole is not created when they vibrate eg. H2, O2, etc
What can the fingerprint region of an infra-red spectra be used for?
• can be used to identify a particular compound - can be used alongside chemical data and a mass spectra to determine a compound’s structure